The ultimate expression of the genetic makeup of a cell resides in its proteins. When and how much of a protein will be synthesized depends on RNA molecules, which not only direct the process, but also constitute the machinery which assembles the proteins from amino acids. Thus, understanding RNA metabolism is a prerequisite for elucidating gene expression in normal cells and for clarifying what has gone wrong under a variety of pathological conditions, many of which are manifested by abnormal gene expression. While considerable information has accumulated about the ribonucleases (RNases) essential to RNA metabolism, much remains to be learned about their complete number, about their physiological roles, about their mechanism of action, and whether and how they might be regulated. It is the long term goal of this project to define the enzymes, pathways and regulatory factors that constitute the totality of RNA metabolism in a single cell. As RNA metabolism is remarkably similar in all cells, our studies continue to be carried out using the model organism, Escherichia coli, for which a large amount of information is already available. Our specific aims are: 1) Examination of the pathway of stable RNA degradation under conditions of stress, and comparison with that of RNA quality control; 2) Analysis of the novel regulatory process determining RNase R levels in cells; 3) Elucidation of the physiological roles of RNase BN and RNase D; 4) Determination of the substrate specificity and mode of action of RNase BN; and 5) Identification of additional RNases participating in maturation of rRNA. To accomplish these aims we will use a combination of approaches involving biochemical, molecular biological, genetic, physiological and immunological procedures. We anticipate that the studies detailed in this proposal will provide important, new information on the enzymes, factors and processes that encompass RNA metabolism.